People with recessive dystrophic epidermolysis bullosa (RDEB) are plagued by painful blisters on the skin, mouth and throat, caused by the slightest trauma, that can expose the body to deadly infection and, in some cases, an aggressive form of cancer.

With the new treatment, "there was improved healing, fewer blisters, and their quality of life was positively affected. They could do things they couldn't do before, like ride a bicycle or go on a trampoline," coauthor Dr. John Wagner of the University of Minnesota said in a telephone interview.

In addition, the improvement has progressed with time, he said. All showed improvement within 100 days, although the pace varied widely from person to person, he said.

But the treatment, as with any bone marrow transplant, carries extraordinary risks, he said. One child apparently died from side effects of a drug used to prepare for the transplant. Another died from infection after the first transplant attempt failed.

For that reason, said Wagner, only the sickest patients with the rare condition - affecting 1 in 50,000 - have been considered candidates for a transplant.

Details of the first seven attempts were reported in Thursday's New England Journal of Medicine. Wagner said six other children have subsequently been treated with good results.

Research is underway to try to isolate the cells of the bone marrow that are best able to fix the defect and join the layers of skin.

The treatment is expensive, costing $500,000 to $1 million. But routine care for such children already costs about $30,000 a year, and because they typically require frequent hospitalizations, the price tag is usually much higher.

"These kids have horrible pain, chronic infections of the skin, multiple hospitalizations, and systemic infections," he said. "They frequently can't eat or refuse to eat because of the pain. Often they die of chronic malnutrition and chronic blood loss."

Coauthor Dr. Jakub Tolar, also of the University of Minnesota, said the treatment is unique because it shows for the first time that the effects of a bone marrow transplant can extend beyond the blood.

"What we have found is that stem cells contained in bone marrow can travel to sites of injured skin, leading to increased production of collagen, which is deficient in patients with RDEB," Tolar said in a statement.

In an editorial in the Journal, Dr. Lenna Bruckner-Tuderman of University Medical Center in Freiburg, Germany, said the therapy represents a leap forward, but expressed caution.

Because the disease can wax and wane, "it is difficult to determine how much of the clinical improvement in the children was due to transplantation and how much was due to a long period of careful medical attention, protection from trauma, and standardized wound care," Bruckner-Tuderman said.